BAK-4 VS BK-7 prism glass in binoculars: what to choose?

If you haven’t heard already there are two types of prisms among many others. The BAK-4 and the BK-7. We will provide an in-depth study into what both of these binoculars entail so you can make the best choice.

What are BK 7 and BAK 4 Prisms?

Firstly, you need to know what these prisms are and what they are made of. BAK-4 is a superior quality prism as it is made of Barium Crown glass. This is known as the best type of prisms to exist out there and why so many people prefer this over the BK-7.

bak-4 prism made of Barium crown glass

This glass has a higher refractive index than the BK-7 as it transmits light in a much better way. What this results in is a higher quality image of what you are trying to see.

On the other hand, the BK-7 prism is made of Borosilicate Crown glass and is considered to be a lower quality glass than BAK-4. This is the type of prisms that you will find in most of the binoculars as the glass is a lower quality which makes it cheaper to sell.

The main difference in both these prisms is that of the glass quality and the anti-reflective coating. Many people don’t prefer BK-7, especially people who love binoculars because it creates blurred edges. On the other hand, the edges of the BAK-4 prism are perfectly round and clear.

This may not be a problem during the day but as the light fades you will start to notice the lower quality of the BK-7 prism. This is because as the level of light reduces the quality of the images will also reduce with the light.

This is why BAK-4 is considered a higher quality prism because it maintains its image quality throughout the day.

Are Bak-4 binoculars always superior BK-7 in image quality?

BK-7 is allawable

Many people wonder if they should avoid the BK-7 prism altogether. However, this entirely depends on what you want from your binoculars. If you want a pair of binoculars that have power till 8 times then you can go for a BK-7 prism if you don’t want to break the bank.

This is because the higher the magnification, the narrower the FOV will become. This is why you should not buy a BK-7 at all if you want higher magnification. It is still allowable when it is till 8x.

It is also a good choice if your budget is stringent and you don’t want to spend too much but still need the binoculars of sufficient quality. This then becomes a great option on a budget.

Pros of BAK-4 prism binoculars

  • High-quality optical glass
  • Bright, realistic colors
  • Perfectly round exit pupil
  • Higher quality of the image even during the night
  • Light transmission properties are unmatched

Cons of BAK-4 binoculars

  • Expensive
  • Not ideal for people who don’t use binoculars much

Pros of BK-7 prism

  • Affordable
  • The quality of the image is still acceptable
  • Widely available

Cons of BK-7

  • Circumcised exit pupils
  • Colors are not so good
  • Image quality starts getting worse as the daylight fades

Is Chinese BAK-4 prism equal to Schott BAK-4 glass?

No, it is not. This is because these two have a completely different glass. The Chinese BAK-4 is not a glass that is made of Barium Crown. It is made up of what is known as a phosphate crown. This is why the Chinese BAK-4 is lower in quality than the Schott BAK-4 glass that is made up of Barium Crown glass.

Apart from that the bubble density of the Chinese BAK-4 is also two times more than the Schott BAK-4 glass. However, one surprising thing you will find is that both these cost the same even though the Chinese BAK-4 is lower in quality and completely different.

So if you are going to make an informed purchasing decision then it is better to go for the Schott BAK-4 as you get the original materials for the same price.

Other than that between BAK-4 and BK-7, BAK-4 is the winner in all aspects.

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2 Replies to “BAK-4 VS BK-7 prism glass in binoculars: what to choose?”

  1. Cristian

    Salve quindi su quali binocoli usano le lenti Schott BAK-4 ? Danmo 10×50 , Nikon aculon a 211 10×50 , Olympus DPS 10×50 , Celestron G2 10×50 ??

    • admin

      Hello, Cristian!
      The lenses of Nikon Aculon are made of Eco-glass.
      Danmo 10×50 uses BAK-4.
      Olympus DPS 10×50 most probably uses BK-7.

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